Generally, phosphor layers of blue, green and red are arranged in the shape of dots or stripes on an inner surface of a face panel of a color display such as a color cathode ray tube, and electron beams collide with the phosphor layers to cause their phosphors to emit light in respective colors, thereby displaying an image.
Conventionally, for the purpose of improving the brightness, contrast and luminous chromaticity of such a color display, there has been employed a method of coating the surface of a phosphor particle with pigment particles of each color which transmit light of the same color as its luminous color, or a method of providing, between a phosphor layer and a face panel, a color filter composed of a pigment layer of each color which transmits light of the same color as the luminous color of the phosphor layer.
It is possible to use an organic or inorganic pigment as a phosphor coating or color filter forming pigment, but there is a limit in usable pigments because of their optical characteristics, heat resistance or toxicity. More specifically, organic pigments, which are excellent in optical characteristics but inferior in heat resistance, cannot be used for color displays including a cathode ray tube which require a heat treatment step. Further, cadmium pigments of the inorganic pigments exhibit good optical characteristics and heat resistance but cannot be used because of its toxicity.
Therefore, as a red pigment for a phosphor coating or color filter of a color display, red iron oxide (Fe2O3), which is excellent in heat resistance and nontoxic, has to be used though it is somewhat inferior in optical characteristics.
However, since red iron oxide has optical characteristics of greatly absorbing wavelengths within the ultraviolet region, the light exposure to a photoresist is decreased in a step of forming a phosphor layer and the like when the surface of a phosphor is coated therewith or a color filter is formed therewith. In other words, in the formation of a phosphor layer by the photolithography, the phosphor coating film or the color filter containing red iron oxide absorbs a part of ultraviolet rays which are applied to cure a photoresist, thus presenting a problem that the photoresist is not sufficiently irradiated with ultraviolet rays.
Accordingly, a phosphor coating and color filter material is demanded which is excellent in optical characteristics, heat resistance, and non-toxicity, and never interferes with the irradiation of a photoresist with ultraviolet rays in forming a phosphor layer and the like.
The present invention is made to solve these problems and it is an object of the invention is to provide a phosphor or color filter which is excellent in optical characteristics, heat resistance and non-toxicity, and never interferes with the irradiation of a photoresist with ultraviolet rays in forming a phosphor layer and the like.
Further, it is another object of the invention to provide a color display which includes the phosphor or color filter and exhibits good luminous chromaticity and excellent display characteristics such as brightness and contrast.